1. Field of the Invention
The present invention relates to a camera shutter which is capable of forming two types of exposure openings different in size from each other by reversing the starting directions of a plurality of shutter blades when they are to be opened.
2. Description of the Related Art
There have been proposed shutters of the type capable of switching between two exposure openings different in size for use with low cost still cameras. These shutters operate by changing emulsion speed of the film to be used with a single shutter speed which is kept unchanged. For example, the shutter opens to a certain side for one speed film, but opens to a different size for a second speed film. From the viewpoint of construction, these shutters are classified into two types: one type uses two driving sources, one for operating the shutter blades and the other for switching exposure opening diameters respectively. The second type uses as a driving source, a single pulse-motor which is reciprocally rotated in directions reverse to each other for switching exposure openings different in size from one to the other (See Japanese Patent Preliminary Publication No. Sho 60-249123).
The camera shutter of the former constructional type, which is equipped with the two driving sources for performing the shutter functions, has a defect that it requires a large number of parts, a large number of assembly stages, etc., thereby increasing manufacturing cost and decreasing the reliability of the shutter itself. On the other hand, the camera shutter of the latter constructional type requires rotating the pulse motor in both the normal and reverse directions for exposure of film and must use a complicated electrical circuit, thereby increasing manufacturing cost of the electrical system and this increasing manufacturing cost of the shutter itself.